9/10 its a driver problem, reinstall your modem drivers, find updated drivers, install a usb filter patch if you have a via compatiable motherboard, download the latest 4-1 driver compilation, post this problem on http://www.dslnuts.com, or http://www.speedguide.net they are more connection specific

had the same problem when i started to use this dsl connection. Problem was indeed the router firmware...
Also noticed that if you run Norton Internet security it could cause a bouncing of traffic. Make sure you configure that well for p2p software...